what would you do?

What would you do if you bought a amp from supposedly reputable dealer and found out a year and a half later it wasnt the amp you bought at all but one of a totally different serial number and ? Wouldnt you think the dealer would know sometimes in that time period they sold the wrong amp to you? I the consumer am only buying one item if he has several amps similar he logs them by serial number therefore he knew he sold the wrong amp but said nothing, how is that even legal? it's a sad day when you cant trust the dealers on audiogon.